Internal combustion engines having a relatively small number of cylinders provide automobile makers with an attractive solution to the need for improved fuel economy. In order to compensate for reduction of cubic capacity, vehicle manufacturers developed technologies to improve engine power, such as direct fuel injection, turbocharging, and variable timing for inlet and exhaust camshafts. In this way six- and eight-cylinder engines can be scaled down without losing available horsepower.
An undesirable consequence of engines with a small number of cylinders is high crankshaft torsional vibration and high engine block vibration caused by forces, such as first and second order forces, that are not cancelled. Such vibrations are ultimately transmitted through the engine mounts and to the vehicle structure.
Engineers managed these vibrations to one extent or another through a variety of approaches, many of which increase the cost of construction and reduce fuel economy. One accepted solution to overcome excessive vibration is the provision of one or more pendulums on the crankshaft to lower the torsional vibration of the crankshaft and the consequent block vibration. Such crankshaft-mounted pendulums function as vibration absorbers as they are tuned to address and thus cancel out vibrations generated by crankshaft rotation, thus smoothing torque output of the crankshafts. This approach is taken as well by designers of some airplane piston engines where the pendulums smooth output torque and reduce stress within the crankshaft itself.
An example of a pendulum vibration absorber associated with an engine crankshaft is set forth in U.S. Pat. No. 4,739,679, assigned to the assignee of the instant application. According to the arrangement set forth in this patent, a pendulum includes an inner curved cam follower surface that is alternately engaged and disengaged from a pin type cam fixed on the pendulum carrier. The crankshaft pendulum is interconnected with the pendulum carrier by pairs of rollers that are movable on mating curved tracks. While there are a number of variations of the movable relationship between the pendulum and the cycloid surface of the crankshaft it is common to incorporate rolling pins as the points of contact between these two components.
While providing an effective solution to the problem of vibrations in smaller internal combustion engines the pendulum crankshaft requires high strength hardened steel on which the rollers can roll. To satisfy this requirement the entire crankshaft must be formed from high grade steel to meet the hardness requirements for the cycloid surfaces. Attempts to harden only the surface of the cycloid sometimes result in distortion of the crankshaft. Beyond the prohibitions created by material costs for an all-hardened steel crankshaft, the labor and tooling required to machine a cycloid into the crankshaft is also expensive.
Thus a new approach to the pendulum crankshafts is needed to address the problems associated with known arrangements.